The invention pertains to an appliance for the thermal processing of granular material, wherein the material to be processed lies on a perforated base, a gas flows through the base from below, and the exhaust gas can be fed behind the fluidized bed to a cyclone separator for the separation of entrained solid particles. In particular, the invention pertains to an appliance for roasting food items such as coffee beans, nuts or almonds, so that in the following description, the topic is usually a coffee roaster, but this does not imply a restriction.
In the processing of coffee it is essential that it be roasted. Thus, there are roasting appliances that can thermally process the raw coffee until it attains the desired degree of roasting. Such roasting appliances can be divided into discontinuously and continuously roasting ovens. For great quantities, it is often practical to use continuously roasting appliances. Such roasting appliances are known, e.g., from EP 0 756 145 A2, EP 0 965 279 A2 or U.S. Pat. No. 4,419,834 and EP 0 137 556 A1.
In the discontinuously roasting process, a predetermined quantity of the material is subjected to the necessary temperature over the desired time duration. Contact roasters are frequently employed. Here, relatively high temperatures are required in order to ensure that the filled charge is fully roasted through and through. It is also known that the material can be charged from below so as to establish a fluidized bed. Then it is also possible to roast at lower temperatures. In such roasting ovens it is necessary for the entrained solid particles, the so-called chaff, to be removed from the gas flow in a separator following the fluidized bed. For instance, a roasting appliance is known from U.S. Pat. No. 5,292,005, in which a cyclone separator is arranged above the fluidized bed. However, such a roaster is very tall.
Fundamental to the invention is an objective to design a discontinuously functioning appliance of the type described in the introduction, which is as compact as possible. In addition, both the thermal losses and the pressure losses should be kept as low as possible.
The objective is realized according to a first embodiment of the invention in that the sieve base is located in an inner chamber, which is at least partially enclosed in an outer chamber forming the cyclone separator, and into which the exhaust gas can be fed from the top in a rotary flow.
According to a second embodiment of the invention, the sieve base is located in an outer chamber, in which at least the area above the perforated base is designed as the cyclone separator. The outer chamber at least partially encloses an inner chamber, through which the gas can be fed from beneath the perforated base into the outer chamber in a rotary flow.
Common to both designs is the fact that the cyclone separator and the roasting chamber are arranged in a common housing. The housing is wider than it is tall, so that the appliance can be readily installed in rooms with ordinary dimensions. Furthermore, this construction results, on the one hand, in minimal surface area, so that the thermal losses can be kept low. On the other hand, the flow paths are short, so that the pressure loss is minimized. In particular, no pipe conduits and the like are required for the gas, which partially determine both the thermal losses and the pressure losses.
Fundamentally, the fluidized bed can be produced by inlet gas. According to one preferred embodiment of the invention, the flow in the lower or the upper area of the inner chamber is connected to that in the outer chamber, so that at least part of the gas is in circulation. This has the advantage that a constant warming of the gas is avoided and energy consumption is optimized.
It is favorable if the outer chamber and/or the inner chamber have essentially circular cross sections. Here, it is practical if the outer and the inner chamber are concentric to each other. In this way, especially for the outer chamber forming the cyclone separator, optimal flow conditions are realized for the exhaust gas, which flows in the essentially annular outer chamber around the inner chamber from the outlet to the inlet of the inner chamber.
It is practical if there is a ventilator to generate the rotary flow in the upper or the lower area of the inner chamber. The intake side of the ventilator is connected to the inner chamber while its pressurized side is connected to the outer chamber. The ventilator can be designed as a radial aerator with its aerator wheel coaxial to the inner and/or the outer chamber. Such an aerator is easy to install and produces the desired rotary flow in the outer chamber. Further, in the case of installation in high or low areas, the motor can remain outside the roaster, which is advantageous in respect to heat generation and accessibility for maintenance.
Furthermore, there can be guide baffles in the gas flow between the walls of the inner and the outer chambers, which reinforce the formation of the rotary flow. Thereby an intensified rotation of the exhaust gas can be produced as it flows through the outer chamber to the inlet of the inner chamber in order to better separate the solid particles.
Normally there is at least one heating device in the gas flow outside the fluidized bed in order to heat the gas to the desired temperature. In the case of the second embodiment with the perforated base in the outer chamber, especially for larger roasters, the heating device can include at least one burner with a flame tube which passes into the inner chamber from above. The flame tube can extend far into the inner chamber and it can have at least one opening, through which at least a partial flow of the returning gas makes its way into the flame tube for after burning. This makes it possible to heat the gas directly without affecting the roasting material. Nevertheless, the roaster appliance remains compact, since the burner requires hardly any additional installation space.
The heating device can include at least one burner, which opens tangentially into the outer chamber. Thereby the rotary flow can also be reinforced in the outer chamber. This arrangement is especially advantageous in the case of larger roasters with the perforated base in the inner chamber.
Especially for smaller roasters, it is practical for the heating device to consist of electrical heating elements. The heating elements can be designed as heating rods in the outer chamber or, e.g., as heating coils mounted in the inner chamber.
According to the physical requirements, solids are carried radially outward in the cyclone separator. It is practical for the outer chamber to have at least one radially outward opening for removal of the separated solid particles. This opening can be opened shortly before the end of the roasting process but also periodically or constantly during the roasting process. An accumulation of the solids is then avoided.
Especially in the case of the embodiment with the perforated base located in the inner chamber, the base is relatively difficult to access for filling or emptying. Consequently, the perforated base can be at least partly collapsible for removal of the material. The roasted material can then be removed from the inner chamber, while the outer chamber has a corresponding removal opening below the inner chamber. In the case of the first embodiment with the interior perforated base, this area of the outer chamber is also readily accessible.
Fundamentally, a collapsible perforated base is also possible in the embodiment with the perforated base in the outer chamber. But an outer opening in the side wall of the outer chamber at the level of the sieve base is also adequate. For emptying, this is merely opened and the roasted material automatically drops out of the opening due to the rotary flow.
Furthermore, it can be advantageous if the outer wall of the outer chamber or the walls of both chambers are at least partially transparent. This has the advantage that the roasting process can be observed. Especially for smaller roasters it is possible for the walls to made of glass. An attractive outer appearance is effected, so that the roaster can be set up for monitoring purposes in coffee shops and the like.
The roaster according to the invention is equally suitable for small and large charges. For larger charges, the use of gas burners to produce the necessary thermal energy is meaningful. For smaller charges, the use of electrical heating energy can be more favorable. The course of the gas flow is always uniform and reduced to a minimum. In the case of the first embodiment, the gas flows from below, through the perforated base, and into the inner chamber. In the ventilator mounted above this section, a rotary flow is produced from top to bottom in the outer chamber. There, the gas again enters the inner chamber. In the other embodiment, a rotary flow from the bottom to the top is produced by a ventilator adjoining the lower part of the inner chamber. The rotary flow produces a fluidized bed above the perforated base in the inner chamber and flows from above back into the inner chamber. Thus, there is always a rotary flow behind the fluidized bed, which effects the expulsion of the undesirable solid particles.